This invention relates to a discharge lamp lighting circuit using a common starter circuit to a plurality of discharge lamps to start the discharge lamps.
The configuration of a lighting circuit of a discharge lamp, such as a metal halide lamp, comprising a DC power supply circuit, a DC-AC conversion circuit, and a starter circuit is known, for example.
As the configuration of the starter circuit, a capacitor and a switch element are provided for a primary winding of a transformer and a high-voltage start (pulse) signal is applied to a discharge lamp via a secondary winding of the transformer. That is, when terminal voltage reaches a threshold value as the capacitor in the primary circuit is charged, the switch element conducts (or breaks down) and the generated voltage at this time is increased by the transformer and is supplied to the discharge lamp as a start signal (so-called starter pulse), causing the discharge lamp to break down.
By the way, to light a plurality of discharge lamps by the lighting circuit in the related art, the starter circuits are provided in a one-to-one correspondence with the discharge lamps, thus causing costs to rise and a unit to be upsized; this is a problem.
For example, to use a discharge lamp as a light source of a car""s front light, if a front light is attached to each of the left and the right of the front of the vehicle, two left and right discharge lamps and their respective lighting circuits become necessary. To adopt a configuration wherein high and low beams are provided by separate discharge lamps (so-called four-light illumination), two left and two right discharge lamps and their respective lighting circuits are required. In such a case, if as many separate starter circuits as the number of the discharge lamps are provided, costs are increased and in addition, as a unit is upsized, it becomes difficult to provide a circuit unit placement space.
It is therefore an object of the invention to reduce costs and miniaturize a unit by providing a common starter circuit to a plurality of discharge lamps.
To the end, according to the invention, there is provided a discharge lamp lighting circuit using a common starter circuit to a plurality of discharge lamps to start the discharge lamps. In the discharge lamp lighting circuit,
(a) the starter circuit has a transformer comprising a plurality of secondary windings provided for one primary winding, the secondary windings being connected to the discharge lamps in a one-to-one correspondence; and
(b) a primary circuit containing the primary winding of the transformer comprises a capacitor and a switch element and when the switch element conducts (or breaks down), the capacitor is discharged and the generated voltage at this time is increased by the transformer, then is applied through each secondary winding to the corresponding discharge lamp.
According to the invention, the transformer implementing the starter circuit comprises a plurality of secondary windings provided for one primary winding and a start signal is applied from each secondary winding to the corresponding discharge lamp, so that the starter circuit can be used in common to a plurality of discharge lamps.